1. Field of the Invention
This invention relates to a rotation shaft seal, especially, a rotation shaft seal used to seal high-pressure fluid such as gas.
2. Description of the Related Art
Conventionally, a rotation shaft seal 31 as shown in FIG. 16, having a cross-sectional configuration of a rubber lip 33 touching a surface of a rotation shaft 32 extends from an outer case 34 toward a sealed fluid side C as to be approximately L-shaped, is used (refer to Japanese patent provisional publication No. 2003-97723, for example). That is to say, the rotation shaft seal 31 is provided with the outer case 34 having an inner brim 36 on an end portion of the sealed fluid side C, a rubber member 37 is united with the outer case 34 by adhesive or brazing as to surround the inner brim 36 of the outer case 34 and cover a peripheral face of the outer case 34. And, a supporting metal 38 having an L-shaped cross-sectional configuration supports the rubber lip 33 on a low pressure side E and the inner peripheral face side (on a back), and a lip end portion 33a is on a position on an axis direction greatly apart from an axis-orthogonal face P0 including the inner brim 36 of the outer case 34. That is to say, a sliding portion S0 exists on a position on an axis direction greatly apart from the axis-orthogonal face P0 including the inner brim 36, and the rubber lip 33 is in a configuration having a cylindrical extension 33c supported by a cylinder portion 38a of the supporting metal 38.
And, conventionally, in this kind of rotation shaft seals, efforts have been paid in design and production to make the end portion 33a of the lip 33, namely, the sliding portion S0, uniformly sliding on the rotation shaft 32 in the peripheral direction. Therefore, the cylinder portion 38a of the supporting metal 38 is consequently composed of a smooth cylindrical wall portion to have an accurate circular cross section.
In a high-pressure state in which high pressure works on a sealed fluid chamber 39, as shown in FIG. 3B, the cylindrical extension 33c of the rubber lip 33 is compressed and deformed, rubber flows (moves) in an arrow F direction for the supporting metal 38 stopping the rubber, the lip end portion 33a also receives the pressure from the sealed fluid side C, and the rubber loses flexibility because inner stress of the rubber concentrates right on the sliding portion S0. Large contact pressure (pressure) P as shown in FIG. 3B is generated on the sliding portion S0 because the contact pressure is generated by pressing to the rotation shaft seal 32 through the rubber of the area on which the inner stress concentrates. And, sealed fluid (lubricant oil included in the fluid) hardly intrudes on the surface between the rotation shaft 32 and the sliding portion S0 because of the above-mentioned large contact pressure P, and abrasion on the sliding portion So of the lip end portion 33a is promoted thereby. Then, the abrasion proceeds as to bite into the sliding portion S0, tightness (sealability) of the seal is rapidly deteriorated, and outer leak of the fluid is generated.
And, in FIGS. 9C and 10C showing the conventional example, the lip end portion 33a (the sliding portion S0) contacts the whole periphery (360°) of the rotation shaft 32 uniformly with large contact pressure P as shown in FIG. 10C when the high pressure works on the sealed fluid chamber 39. The lubricant oil in the sealed fluid hardly intrudes on (being induced to) the surface between the rotation shaft 32 and the sliding portion S0, abrasion on the sliding portion S0 of the lip end portion 33a is promoted, the abrasion proceeds as to bite into the sliding portion S0, tightness (sealability) of the seal is rapidly deteriorated, and outer leak of the fluid is generated. In other words, under a high-pressure circumstance, adding to the strong pressing of the end portion 33a of the rubber lip 33 to the rotation shaft 32, the end portion 33a is uniformly pressed to the whole periphery of the rotation shaft 32, the lubricant oil in the fluid such as a cooling medium can not intrude on the surface of the sliding portion S0 and the rotation shaft 32, frictional resistance is increased, heat is generated, and the sliding portion S0 is rapidly abraded.
It is therefore an object of the present invention to provide a rotation shaft seal, with which the contact pressure of the rubber sealing portion on the contact portion on the rotation shaft is restricted as not to be excessive, having long life for sealing high-pressure gas.